A CBS instant poll of undecided voters found 37 percent gave the advantage to Obama, while 30 percent sided with Romney. The remainder -- 33 percent -- thought it was a tie, according to CBS' Mark Knoller.

A majority of CBS' respondents -- 56 percent -- said Obama would do a better job helping the middle class, compared to 43% who said they believe Romney would. But on who would handle the economy better, Romney came out ahead, 65 percent to 34 percent.

Such polls are meant to take a quick snapshot rather than make any definitive prediction about how the debates will play when all is said and done. But they can suggest which way they are headed. CNN and CBS were split on who won the vice presidential debate, one siding with Joe Biden and the other with Ryan. For the first presidential debate, both gave the win to Romney.

Correction: An earlier version of this post misstated CNN results for Romney.